As concerns over maintaining proper health continue to grow, vitamin and antioxidant use and intake also continue to rise. As more evidence of the potential benefits associated with the use and intake of vitamins and antioxidants continues to be generated, demand for such substances increases, as does the demand for purer forms thereof. Many antioxidants and vitamins can be found in, and extracted from, natural sources. However, these natural sources, e.g., plants and vegetables, contain many undesirable components and impurities which are extracted along with the antioxidants.
For example, tocopherol compounds are components of vegetable oils which exhibit vitamin E activity. Tocopherol compounds are found widely distributed in many organic substances, including grain oils and vegetable oils. However, the amount of tocopherol present in the natural oils may be small, and therefore, the oils are distilled to concentrate the tocopherol content. Unfortunately, the content of other undesirable co-boilers, as well as pesticides, fertilizers, etc. may also be concentrated.
As such, there have been many attempts to recover and purify antioxidants, such as tocopherols, from natural sources. For example, a method which involves mixing a tocopherol-containing material with a polar organic solvent and contacting this mixture with a strongly basic anionic exchange resin, whereby the tocopherols are absorbed onto the resin, and subsequently eluted with an acidic solution, has been described. However, such methods can result in resin fouling, and potential oxidation of the resins may result in a persistent amine odor. Moreover, resins are short-lived, expensive and provide relatively low capacity.
Other processes for the isolation of tocopherols involve treating deodorizer distillates, which comprise the xe2x80x9csludgexe2x80x9d or distillate obtained in connection with the production of edible oils and fats subsequent to the deodorization step, with a lower aliphatic alcohol in the presence of an acid catalyst, often with prior saponification of the sludge, for the purposes of esterifying the free fatty acids present in the sludge. Other processes have been disclosed wherein the tocopherols and/or sterols are esterified with the free fatty acids contained in the distillates. However, these processes are often complicated, time-consuming and expensive. Moreover, most prior art processes for the purification or isolation of tocopherols and/or sterols which involve the esterification of the tocopherols and/or sterols with free fatty acids present in the feed are incapable of adequately removing impurities and other components which co-distill with tocopherols and/or sterols, at sufficient yields.
Another process for the separation of tocopherols has been described wherein borate esters are formed, the mixture is distilled and the esters are subsequently hydrolyzed, with subsequent separation of the borate source from the tocopherol. While such a process generally removes a large portion of the impurities that co-distill with the tocopherol, significant amounts of the tocopherol in the original feed material can be lost during the purification, foaming during the esterification process is a significant problem, and undesirable borate solids can form requiring additional separation steps.
Thus, there is a need in the art for a process by which tocopherol and/or sterol compounds can be purified in high yield from natural sources with suitably high degrees of purity.
The present invention relates to processes for the purification of compounds, such as tocopherol and/or sterol compounds, from natural sources, wherein a high yield is obtained, in addition to a high degree of purity. The processes according to the present invention provide purified tocopherols and sterols from natural sources at unexpectedly high and significantly improved yields and further remove many of the unwanted components which co-distill with tocopherols and/or sterols, as well as impurities and other undesirable components to negligible amounts and even undetectable levels.
The present invention includes a process for purifying compounds, wherein the process comprises: (a) providing a first mixture comprising at least one compound selected from the group consisting of tocopherol compounds and sterol compounds, and an alcohol having from about 10 to about 30 carbon atoms; (b) reacting the first mixture with one or more boron-containing compounds selected from the group consisting of boric acid, alkoxy borates, alkoxy boroxines, phenoxy borates and phenoxy boroxines to form a second mixture comprising one or more orthoborate esters, wherein the mole ratio of combined tocopherol, sterol and alcohol to boron is at least about 2.5:1; (c) heating the second mixture to remove low boiling point components to form a residue comprising the one or more orthoborate esters; (d) contacting the residue with one or more compounds capable of solvolyzing the one or more orthoborate esters to form a third mixture comprising one or more resulting boron-containing compounds, the alcohol and the at least one compound selected from the group consisting of tocopherol compounds and sterol compounds; and (e) recovering the at least one compound selected from the group consisting of tocopherol compounds and sterol compounds.
In accordance with preferred embodiments of the present invention, the alcohol comprises oleyl alcohol or dodecyl alcohol, the boron-containing compound comprises boric acid, the mole ratio of combined tocopherol, sterol and alcohol to boron is at least about 3:1; and step (c) is carried out at a temperature which is about 60xc2x0 C. greater than the boiling point of the at least one compound selected from the group consisting of tocopherol compounds and sterol compounds, under reduced pressure.
The present invention also includes a process for purifying compounds, said process comprising: (a) subjecting a composition comprising at least one compound selected from the group consisting of tocopherol compounds and sterol compounds to an activated carbon pretreatment; (b) combining the pretreated composition with one or more boron-containing compounds selected from the group consisting of boric acid, alkoxy borates, alkoxy boroxines, phenoxy borates and phenoxy boroxines to form a mixture comprising one or more borate esters; (c) heating the mixture to remove low boiling point components to form a residue comprising the one or more borate esters; (d) contacting the residue with one or more compounds capable of solvolyzing the one or more borate esters to form a second mixture comprising one or more resulting boron-containing compounds and the at least one compound selected from the group consisting of tocopherol compounds and sterol compounds; and (e) separating the one or more resulting boron-containing compounds and the at least one compound selected from the group consisting of tocopherol compounds and sterol compounds.
Furthermore, the present invention includes a composition comprising a mixture of trialkyl orthoborate esters, dialkyl-monotocopherol orthoborate esters, and monoalkyl-ditocopherol orthoborate esters. A composition in accordance with the present invention may further comprise dialkyl-monosterol orthoborate esters, monoalkyl-disterol orthoborate esters and monoalkyl-monotocopherol-monosterol orthoborate esters. Additionally, the present invention includes a composition prepared by a process comprising: (a) combining a composition comprising at least one compound selected from the group consisting of tocopherol compounds and sterol compounds with an alcohol having from about 10 to about 30 carbon atoms to form a first mixture; (b) reacting the first mixture with one or more boron-containing compounds selected from the group consisting of boric acid, alkoxy borates, alkoxy boroxines, phenoxy borates and phenoxy boroxines to form a second mixture comprising one or more orthoborate esters, wherein the mole ratio of combined tocopherol, sterol and alcohol to boron is at least about 2.5:1; and (c) heating the second mixture to remove low boiling point components to form a mixture comprising the one or more orthoborate esters.
The present invention is directed to processes for the purification of compounds such as, for example, tocopherol compounds and sterol compounds. As used herein, the term xe2x80x9ctocopherol compoundsxe2x80x9d refers to the broad class of compounds which can be characterized as derivatives of 6-chromanol having an isoprenoid side chain, of which many are known to exhibit vitamin E activity. These compounds include, for example, the alpha (xcex1:-), beta (xcex2-), gamma (xcex3-) and delta (xcex4-) homologues of tocopherol, as well as unsaturated derivatives, such as, tocomonoenols, tocodienols and tocotrienols. As used herein, the term xe2x80x9csterol compoundsxe2x80x9d refers to the broad class of compounds also known as steroid alcohols, which possess a steroid nucleus of four fused carbon rings with a hydroxyl group present in addition to any other side chains, for example, an 8 to 10 carbon side chain. As used herein, xe2x80x9csterol compoundsxe2x80x9d refer to both plant- and animal-derived steroidal alcohols, including, for example, cholesterol and phytosterols including, but not limited to, sitosterol and campesterol, as well as the hydrogenated versions thereof known as stanols.
Compositions which contain at least one tocopherol compound or sterol compound (hereinafter also referred to as xe2x80x9cstarting compositionsxe2x80x9d) which may be subjected to the purification process in accordance with the present invention include, for example, natural organic sources such as grain oils, vegetable oils and plant sources. Examples of suitable grain and vegetable oils include wheatgerm, corn, barley, rye, safflower, soybean, peanut, cottonseed, linseed, sunflower, rapeseed and palm oils. Examples of suitable plant sources from which the starting composition may be derived include palm leaves, lettuce, alfalfa, rubber latex and a variety of other plant materials. The natural sources for use in the present invention are available commercially and can also be extracted via known techniques.
The amount of tocopherol compound or sterol compound present in such compositions for use in the present invention may vary widely, and may be as low as about 1% prior to purification by the process of the present invention, or as high as at least about 95%. Often, vegetable oils are distilled to produce a concentrate that is up to about 60% mixed tocopherols. Such vegetable oil concentrates can also be used as compositions containing tocopherol and/or sterol compounds to be purified in accordance with the present invention.
A first mixture in accordance with the present invention will contain an alcohol which may be added to a starting composition, or a starting composition which already contains a suitable alcohol may be used. For example, many vegetable oil distillates may contain various fatty alcohols in varying amounts. In some instances, a starting composition may contain some alcohol, and further alcohol may be added to provide a first mixture.
Suitable alcohols, which may be present in a first mixture in accordance with the present invention, either naturally to some degree or by combination with a tocopherol compound and/or a sterol compound, include primary or secondary alcohols, which may be saturated or unsaturated, branched or linear and cyclic or acyclic having from about 10 to about 30 carbon atoms, or phenols. Alcohols used in accordance with the present invention will preferably have from about 12 to about 26 carbon atoms, and more preferably from about 12 to about 20 carbon atoms. Alcohols with less than 12 carbons, such as n-decanol, may be used in accordance with the present invention, however the volatility of the tridecylborate formed during reaction of the alcohol and the boron-containing compound(s) is high enough that large portions of the alcohol are lost along with the co-boiling fraction of the initial starting material during the heating step, leading to lower recovery of tocopherols and/or sterols. Thus, alcohols with 12 or more carbon atoms are preferred. Moreover, alcohols with more than 26 carbon atoms may be used in accordance with the present invention, however separation of the alcohol from the recovered tocopherol and/or sterol becomes more difficult, leading to lower purity. Thus, alcohols with 26 or less carbon atoms are preferred.
The most preferred alcohols for use in accordance with the present invention will have from about 12 to about 18 carbon atoms. Examples of alcohols which may be used in accordance with preferred embodiments of the present invention include, but are not limited to, dodecanol, tetradecanol, hexadecanol, octadecanol, oleyl alcohol, isostearyl alcohol, Guerbet alcohols, particularly C16 Guerbet alcohol (i.e., 2-hexyldecanol), and mixtures thereof Stearyl alcohol, or octadecanol, is an alcohol found in most vegetable oil distillates, and is further preferred since lower amounts will need to be added to a first mixture in accordance with the present invention. Alcohols which can be used in accordance with the present invention are common and well known and can be obtained commercially or prepared via known methods.
In accordance with one embodiment of the present invention, wherein a composition containing a tocopherol compound and/or a sterol compound is combined with one or more alcohols, as described above, to form a first mixture, the composition and the alcohol component may be combined in any manner sufficient to allow mixing of the components. The method of combination and container are not critical, and can include, for example, introducing the components, simultaneously or in any order, into a container with stirring by mechanical agitation. Preferably, the components will be combined in a container which is capable of withstanding the heat applied subsequently in the process according to the present invention, or in a container adapted for facilitated transfer of the materials to a heating apparatus.
In other preferred embodiments of the present invention, a carbon treatment can be used to enhance the overall purification. Carbon treatments in accordance with the present invention can be employed as a pre-treatment, or as a post-treatment. For example, in certain preferred embodiments of the present invention, a starting composition is subjected to an activated carbon pretreatment either prior to combining the starting composition with an alcohol or before reacting the first mixture with the one or more boron-containing compounds. Alternatively, a tocopherol or sterol compound purified in accordance with the present invention can be subjected to an activated carbon post-treatment. An activated carbon treatment in accordance with such preferred embodiments generally includes contacting either the starting composition, the first mixture, or the purified final compounds with an activated carbon powder for at least 1 minute at a temperature of at least about 50xc2x0 C., preferably with stirring. It is preferable that the activated carbon powder be present in an amount of at least about 0.25 weight percent based on the total weight of the compound(s) selected from tocopherol compounds and sterol compounds. Selection between pre- and post-treatment is generally a matter of process convenience, although stirring and carbon contact may be easier with the purified compounds as opposed to the starting compounds or first mixtures.
The first mixture, which includes: (1) the composition containing the tocopherol compound(s) and/or the sterol compound(s) in addition to any impurities present in the composition such as, for example, low boiling point components and co-distilling impurities; and (2) the alcohol component, is reacted with one or more boron-containing compounds.
Boron-containing compounds which may be used in accordance with the present invention include, but are not limited to, boric acid, alkoxy borates, alkoxy boroxines, phenoxy borates and phenoxy boroxines. Preferably, the boron-containing compound used in accordance with the present invention will be boric acid, though other boron-containing compounds such as boroxines, also known as metaborates, may be used so long as the overall ratio of hydroxyl-containing species to boron is maintained at a level in accordance with the present invention. Alkoxy and/or phenoxy borates or boroxines used in accordance with the present invention will preferably have up to 30 carbon atoms, more preferably from about 12 to about 26 carbon atoms, and most preferably from about 12 to about 20 carbon atoms.
Boric acid and alkoxy and/or phenoxy borates or boroxines used in accordance with the present invention can be obtained commercially or synthesized by known methods.
The amount of boron-containing compound reacted with the first mixture is an amount which is sufficient to form essentially orthoborate esters. Thus, in accordance with the present invention, the mole ratio of the tocopherol compound(s), sterol compound(s) and alcohol(s), combined, to boron in the boron-containing compound is at least about 2.5:1. Preferably, the mole ratio is at least about 2.75:1, and most preferably the mole ratio is at least about 3:1. The tocopherol compound(s), sterol compound(s) and alcohol(s) can be used in greater excess, however, the maximum preferred mole ratio of these components, for economical reasons is about 3.5:1. A more preferred maximum mole ratio is about 3.2:1. At mole ratios greater than about 3.5:1, the capacity of a reactor will be reduced. However, larger ratios could be used.
It is essential, in accordance with the process of the present invention, that the mole ratio of the tocopherol compound(s), sterol compound(s) and alcohol(s), combined, to boron in the one or more boron-containing compounds be at least about 2.5:1, in order to form essentially only orthoborate esters of the general formula (I): 
wherein each xe2x80x94OX independently represents a tocopherol, sterol or alcohol residue, bound to the boron atom at its hydroxyl oxygen position, as opposed to metaborate esters or polyborate esters, wherein multiple boron-containing compounds condense to form a heterocyclic boron ester of the general formula (II): 
wherein each xe2x80x94OX is as described above. During the formation of orthoborate esters in accordance with the present invention, competitive reactions may occur if the mole ratio is not kept at or above the levels recited above. For example, competitive dimerization and/or trimerization may occur at lower mole ratios. Thus, for example, where the mole ratio of components is about 2:1, competitive dimerization may occur resulting in polyborate esters of the general formula (III): 
Polyborate esters of the general formula (m) may fuirther break down into esters of the general formulae (I) and (II), along with other monotocopherol/monosterol orthoborate ester species.
Orthoborate esters of the general formula (I), which may be formed during the reaction in accordance with the present invention include monoalkyl-ditocopherol orthoborate esters, dialkyl-monotocopherol orthoborate esters, monoalkyl-disterol orthoborate esters, dialkyl-monosterol orthoborate esters, and trialkyl borate esters, wherein the alkyl moieties correspond to the alcohol in the first mixture. Other orthoborates which may form during the reaction, though to a lesser degree include mixed alkyiltocopherol/sterol orthoborate esters, tritocopherol orthoborate esters and tristerol orthoborate esters.
The second mixture thus formed includes the one or more orthoborate esters, any unreacted alcohol(s), tocopherol compound(s), sterol compound(s), and/or boron-containing compound(s) which may remain, and the remainder of the original composition containing the tocopherol and/or sterol compound(s), namely impurities such as pesticides, fertilizers, co-boiling hydrocarbons, etc. It is preferable to allow the reaction in which the orthoborate esters are formed to proceed as close to completion as possible, and thus maximize the formation of tocopherol and/or sterol orthoborate esters. While the borate esterification process is reversible and will attain one of several equilibria states if allowed, the reaction can be conducted to shift the reaction so as to maximize ester production, as discussed in more detail below, and thus increase the amount of tocopherol and/or sterol ultimately recovered. The borate esterification process will proceed at room temperature. However, the reaction may be carried out more rapidly at an increased temperature. Thus, in accordance with preferred embodiments of the present invention, the esterification reaction may be carried out at temperatures of from about 40xc2x0 C. to about 305xc2x0 C. for a sufficient length of time, and at varying pressures as discussed below. A more preferred temperature is from about 100xc2x0 C. to about 225xc2x0 C., and an even more preferred temperature range is from about 160xc2x0 C. to about 200xc2x0 C. At temperatures in excess of 100xc2x0 C., the condensation water produced during the esterification reaction can be substantially eliminated.
Temperatures during the esterification process should also be maintained below the boiling points of the tocopherol and/or sterol compound(s) in order to minimize the loss of the compounds due to their distillation prior to the formation of the one or more orthoborate esters. Materials less volatile than the tocopherol and/or sterol compound(s) and any co-boiling impurities may preferably be removed during esterification by using the preferred higher temperatures previously set forth.
If desired, in order to aid in the removal of the water and other volatiles during the esterification reaction, the pressure during esterification may be lowered. Thus, in accordance with preferred embodiments of the present invention, the esterification reaction may be carried out at pressures of from about atmospheric pressure to as low as 1 mm Hg, or even lower, for example, 0.1 mm Hg, so long as the temperature is maintained low enough to prevent the distillation of the tocopherol and/or sterol compound(s). Thus, when the pressure during esterification is below 1 mm Hg, the temperature should be maintained at or below about 250xc2x0 C. to ensure that a minimum amount of the tocopherol and/or sterol compound(s) distill. In one preferred embodiment of the present invention, the esterification reaction will be carried out at pressures less than or equal to 5 mm Hg. A particularly preferred embodiment of the present invention includes conducting the esterification at temperatures of from about 110xc2x0 C. to about 130xc2x0 C., under a pressure of from about 1 mm Hg to about 5 mm Hg.
Another option, though not preferred for environmental reasons, which may be employed to assist in the removal of water and other volatiles during the esterification process is the addition of a non-reactive, volatile solvent such as, for example, aliphatic hydrocarbon solvents, aromatics, C3-10 alcohols and mixtures thereof.
Removal of esterification by-products, especially water, is preferred during the esterification reaction as this prevents reformation of the tocopherol and/or sterol compound(s) via hydrolysis of the borate esters prior to removal of the low-boiling impurities. Moreover, as the removal proceeds, the reaction proceeds more towards completion, and the potential loss of tocopherol and/or sterol compound(s) due to premature reformation of these compounds through potential condensation reactions is prevented.
In accordance with the present invention, esterification of the tocopherol and/or sterol compound(s) and the alcohol component with one or more boron-containing compounds, wherein the mole ratio of tocopherol, sterol and alcohol to boron is 2.5:1 or higher, prevents unwanted boron solid formation. Thus, additional boron solid removal or recovery and recycling steps, which may be complicated, costly and/or time-consuming, are unnecessary.
After the esterification reaction is completed or taken as close to completion as is desired, the temperature may be raised in order to heat the second mixture to remove remaining low boiling point components, including impurities which co-boil with the unesterified tocopherol and/or sterol compound(s). The temperature is raised to the extent necessary to remove substantially all components boiling at temperatures below the boiling point of the one or more orthoborate esters.
Temperatures during the heating step should be sufficient to remove all, or substantially all, impurities boiling at temperatures lower than the orthoborate esters, i.e., xe2x80x9clow boiling point componentsxe2x80x9d, including the components of the initial starting composition which have boiling points close to the tocopherol and/or sterol compound(s), i.e., xe2x80x9cco-boilersxe2x80x9d. The precise pressures and temperatures preferably used in accordance with the present invention will vary depending on the distillation points of the impurities present in the composition containing the tocopherol and/or sterol compound(s). Preferred temperatures for the removal of low boiling components, under reduced pressures, are at least about 280xc2x0 C., more preferably at least about 300xc2x0 C., and most preferably at least about 305xc2x0 C. In general, the preferred temperature for removal of low boiling components during the heating step will be from about 60xc2x0 C. to about 70xc2x0 C. above the boiling point of the tocopherol at that particular pressure. The boiling point of a starting composition at a particular pressure can be determined through known thermodynamic calculations. The duration of heating of the second mixture may vary, but will be for a time sufficient to allow for distillation of all, or substantially all, low boiling point components. Thus, the heating is generally continued until distillation, or evaporation of the low boiling point components ceases.
However, when the starting composition contains both tocopherol and sterol compounds and isolation of both are desired, the temperature during the heating step is preferably maintained below about 320xc2x0 C. At temperatures greater than about 320xc2x0 C., the sterol-containing orthoborate esters formed during the esterification step may decompose, allowing the formation of undesired by-products (e.g. sterol hydrocarbons and/or ring-opened tocopherols), thus reducing the quantity of sterol that may be later recovered.
In accordance with preferred embodiments of the processes according to the present invention, the distillation of the second mixture is carried out under reduced pressures. Preferably, the removal of the low boiling point components will be carried out at pressures less than or equal to 5 mm Hg, and more preferably at pressures less than or equal to 1 mm Hg.
As used herein, the phrase xe2x80x9csubstantially allxe2x80x9d shall mean that degree of removal which is considered sufficient with respect to each component by one skilled in the art, and will generally mean removal of all low boiling point components except for small amounts ranging from undetectable to trace quantities. In general, the purity of the hydroxylic components (i.e., tocopherol and/or sterol compound(s)), obtained by the processes in accordance with the present invention will be 95% or greater, preferably 99% or greater, and most preferably 99.9% or greater.
Co-boilers removed in accordance with the present invention include the non-hydroxyl compounds which boil at or near the boiling points of the tocopherol and/or sterol compound(s), including non-tocopherol, non-sterol components found in the natural sources which may be used as starting compositions in accordance with the present invention, such as, for example, natural esters, hydrocarbons, ketones, pesticides, and fertilizers, particularly steryl hydrocarbons and squalene.
After heating the second mixture at a sufficient temperature for a sufficient amount of time, a residue containing the one or more orthoborate esters will remain. The residue is contacted with any one or more compounds capable of solvolyzing (i.e., cleaving) the orthoborate ester(s) to form the third mixture which contains the tocopherol and/or sterol compound(s), one or more resulting boron-containing compounds (i.e., boron-containing products of solvolysis), and the alcohol originally combined with the starting composition containing the tocopherol and/or sterol compound(s). Examples of suitable compounds capable of solvolyzing the orthoborate ester(s) for use in accordance with the present invention include, but are not limited to, water, methanol, ethanol and mixtures thereof Sources of water, methanol and ethanol may also be used. The one or more resulting boron-containing compounds may include boric acid, and/or trialkyl borate esters depending on which compounds are used for solvolysis. Solvolysis via water (i.e., hydrolysis) will produce boric acid, whereas solvolysis with methanol and/or ethanol will produce the corresponding alkoxy borate esters.
The amount of water, methanol and/or ethanol contacted with the residue containing the orthoborate esters is preferably at least about three moles of water and/or alcohol(s) per mole of boron in order to maximize the amount of tocopherol released via solvolysis and available for recovery. The maximum amount of water and/or alcohol(s) used for solvolysis is limited only for reasons of practicality. In preferred embodiments of the present invention, the amount of water, methanol and/or ethanol may range from about 3.5 to 30 moles per mole of boron to ensure complete solvolysis.
Methanol, ethanol and mixtures thereof are preferred compounds capable of cleaving the orthoborate ester(s) due to the ease of removing the reaction products thus formed, namely methoxy and ethoxy borate esters. Removal of the trimethoxy and triethoxy borate esters may preferably be accomplished via azeotropic distillation. The use of azeotropic distillation allows both methanol and ethanol to be continually added for continued hydrolysis of the orthoborate ester(s), thereby maximizing solvolysis while simultaneously forming and removing the trialkoxy borate esters. Preferably, azeotropic distillation is performed to drive the solvolysis to completion. Thus, in a preferred embodiment of the present invention, azeotropic distillation is performed to drive the solvolysis to completion, with further distillation of the remaining azeotropic solvent mixture and any first mixture-alcohol present in the third mixture, allowing for subsequent isolation of the tocopherol and/or sterol compound(s).
The solvolysis may be conducted at room temperature or higher. When water is used, the temperature should be below reflux to allow for maximum solubility of the boric acid formed. The water and boric acid thus formed can be separated from the tocopherol and/or sterol compound(s) via phase separation. The isolated tocopherol and/or sterol containing phase is then preferably washed with water to ensure complete removal of boric acid. Optionally, the first water wash may be cooled, and solid boric acid recovered and recycled.
Water may be used for hydrolysis at temperatures higher than the boiling point of water by applying pressure to increase the reflux point. By increasing pressure, the temperature may be as high as the equipment will allow.
Any remaining water, ethanol, methanol, and/or original alcohol added to the starting composition, which is not removed via phase separation or through azeotropic distillation when performed, may be removed via further distillation of the solvolyzed third mixture. Such further distillation may be performed at any temperature sufficient to remove both (1) the one or more compounds capable of hydrolyzing the orthoborate ester(s) and (2) the original alcohol added to the starting composition, but below the temperature at which tocopherol compounds and sterol compounds distill.
Thus, after solvolysis and removal of any remaining boron-containing solvolysis products (i.e., boric acid and water, or alkoxy borate esters which did not distill oft), the tocopherol and/or sterol compound(s) are recovered. Often, subsequent to solvolysis with accompanying azeotropic distillation, the remaining tocopherol and/or sterol compound(s) are sufficiently pure for further use, and recovery can be performed by simply collecting the tocopherol and/or sterol compound(s).
However, if further purification or enhanced recovery is desired, additional methods including, but not limited to, adsorption chromatography, extraction, ion exchange and fractional distillation of the tocopherol and/or sterol compound(s) may be used.
Where the starting composition contains at least one tocopherol compound and at least one sterol compound and recovery and purification of both is desired, distillation subsequent to recovery can be performed to collect the tocopherol compound(s), thus leaving the sterol compound(s) in the residue.